The patients will receive up to five separate meals. Four of these will be high phosphorus content meals and one will be a low phosphorus content meal. On up to three occasions with the high phosphorus content meals the patients will ingest one of the three phosphate binders. The meals will be ingested after a twelve-hour overnight fast. Labs will be drawn prior to meal ingestion and then at 15, 30, 60, 120 and 240-minute intervals. The labs will consist of iPTH, phosphorus, calcium, and glucose. A serum albumin level will be obtained with the initial specimen only. The patients will have an iPTH level of at least 200pg/ml and a serum phosphorus level of at least 4.0 mg/dl.